A Rising Bubble Ring

T.T. Lim
C.T. Toh
Department of Mechanical Engineering
National University of Singapore
Singapore

M. Cheng
J. Lou
Institute of High Performance Computing
Singapore

Image Credit: T.T. Lim & C.T. Toh (National University of Singapore); M. Cheng & J. Lou (Institute of High Performance Computing, Singapore)A multiple-exposure photograph of a single bubble ring rising to the top of a water tank.

A bubble ring is an underwater vortex ring whose inner rotating region or vortex core is filled with air. Scuba divers and free-divers sometimes create them for their amusement by puffing a burst of air through their mouths. In a laboratory, a commonly used technique is to eject a short burst of air through a small opening at the bottom of a water tank.

The ejected air initially forms a bubble, but this subsequently transforms into a donut or ring shape due to the pressure difference between the top and the bottom of the bubble. The force of buoyancy causes the bubble ring to rise, and another force, called the cross-flow lift force, causes its radius to increase and its velocity to decrease.

The photograph above shows a multiple-exposure image of a single bubble ring rising to the top of a 1.5-meter water tank. The photograph is captured with the aid of a stroboscopic light source located at the top of the tank and with the camera aperture fully opened. The "sparkles" on the three uppermost rings are due to reflection of the stroboscopic light from the bubble's surface.

Reporters and Editors

This image can be freely reproduced with the accompanying credit: "T.T. Lim & C.T. Toh (National University of Singapore); M. Cheng & J. Lou (Institute of High Performance Computing, Singapore)."